BART police can use tasers only if a suspect presents "an immediate threat of bodily harm," SF Weekly reported.

Civil rights attorney John Burris told NBC Bay Area, given what he saw on the video, BART police used excessive force. Burris said the use of the Taser was an overreaction that could have had deadly consequences.

“He might have been loud, but that's not a basis to tase somebody,” Burris said.

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The woman who was sitting next to the man on the train is also highly troubled. She has written a blog about the incident, claiming the man may have been intoxicated but was genuinely nice and wasn't posing a threat. She is suggesting things may have escalated because he's a black man.

BART Police Chief Kenton Rainey says he has ordered an investigation, and while he refuses to draw conclusions, he points out the officer repeatedly asked the man to comply.

“He warned the suspect numerous times again on this video. He's extremely patient and the suspect was not going to comply, so he tased him,” Rainey said.

Rainey also points out the suspect, Robert Asberry, is a parolee who had a warrant out for his arrest. He says a station agent called police after seeing the suspect drunk and harassing customers.

“Most people contacted by police, they don't behave the way this individual did,” Rainey said.

A former BART police officer famously shot and killed Oscar Grant III on New Year's Day 2009 when the officer mistook his handgun for his taser, and BART police most-recently shot and killed a homeless man on the Civic Center station platform in 2011.